Excitation of dielectric barrier discharges by unipolar submicrosecondsquare pulses

Abstract

Dielectric barrier discharges (DBDs) are self-extinguishingdischarges due to charge accumulation on dielectric surfaces. In order to takeadvantage of these surface charges also at a low repetition frequency,high-voltage unipolar square pulses (amplitude up to 15 kV, rise and fall timeless than 20 ns) are applied to drive DBDs. For electrical diagnostics of thisnovel excitation method, a temporally dynamic model for diffuse DBDs isintroduced, from which equations were derived which allow the calculation ofinternal electrical quantities in the discharge gap from measured externalelectrical quantities. It was found, following a primary discharge at therising front or at the top of the voltage pulse, that a secondary discharge isinduced at the end of the falling voltage flank without simultaneouslyconsuming energy from the external circuit. The energy needed is provided bythe accumulated surface and space charges left by the primary discharge, whichare totally or partially lost under normal low-frequency sine or square waveexcitation. Secondary discharges are observed in a wide range of electrodeconfigurations, gases and gas pressures for both homogeneous and filamentarydischarges. In the case of filamentary modes, secondary discharges are foundto develop along the remaining channels of the preceding primary discharges.Experiments for ozone synthesis show an improved energy efficiency of 8-9 eVper ozone molecule, which is about 30% better than that achieved with sinewave excitation.